feat: Expose CompressDictLevel public API from PR valyala#63

Make CompressDictLevel part of the public API instead of being internal.
This allows users to specify both dictionary and compression level
parameters together, which is useful for advanced compression scenarios.

Previously CompressDict used level 0 which barely compresses.

Based on valyala#63

Author: GrigoryEvko

gozstd.go

@@ -48,24 +48,24 @@ const DefaultCompressionLevel = 3 // Obtained from ZSTD_CLEVEL_DEFAULT.
 
 // Compress appends compressed src to dst and returns the result.
 func Compress(dst, src []byte) []byte {
-	return compressDictLevel(dst, src, nil, DefaultCompressionLevel)
+	return CompressDictLevel(dst, src, nil, DefaultCompressionLevel)
 }
 
 // CompressLevel appends compressed src to dst and returns the result.
 //
 // The given compressionLevel is used for the compression.
 func CompressLevel(dst, src []byte, compressionLevel int) []byte {
-	return compressDictLevel(dst, src, nil, compressionLevel)
+	return CompressDictLevel(dst, src, nil, compressionLevel)
 }
 
 // CompressDict appends compressed src to dst and returns the result.
 //
 // The given dictionary is used for the compression.
 func CompressDict(dst, src []byte, cd *CDict) []byte {
-	return compressDictLevel(dst, src, cd, 0)
+	return CompressDictLevel(dst, src, cd, 0)
 }
 
-func compressDictLevel(dst, src []byte, cd *CDict, compressionLevel int) []byte {
+func CompressDictLevel(dst, src []byte, cd *CDict, compressionLevel int) []byte {
 	var cctx, cctxDict *cctxWrapper
 	if cd == nil {
 		cctx = cctxPool.Get().(*cctxWrapper)